I. Lukeš, L. Bláha, F. Kesner, J. Rohovec, P. Hermann:
"Complexing Properties of Diastereoisomers of 1-(L-Methionylamino)-ethylphosphonic Acid."
J. Chem. Soc., Dalton Trans. 1997, 2629-37     > PDF

Abstract:

The acid-base and complexing properties of (S,S) and (S,R) diastereoisomers of 1-(methionylamino)ethylphosphonic acid were studied pH-metrically (25°C, 0.1 mol.dm^-3 KNO₃).  The protonation and stability consts. for complex formation with Co²⁺, Ni²⁺ and Zn²⁺ indicate co-ordination only via the amine, carbonyl peptide and phosphonic groups and, for Cu²⁺, also via nitrogen of the deprotonated peptide amide group.  The presence of the same types of complexes as in phosphonodipeptide series which do not contain sulfur in the amino acid side chain was obsd.  Similarly, the differences found between diastereoisomers correspond to the interaction of the hydrophobic and/or hydrophilic parts of the mol.  Co-ordination via sulfur has not been obsd.  The species detd. by 'out of cell' titrns. of the platinum(II) and palladium(II) systems depend on the initial metal:phosphonic acid molar ratio.  A 1:2 ratio indicates the co-ordination of amine and sulfur in a wide pH region; in the alk. region, sulfur atoms are replaced by the peptide amide group.  A 1:1 ratio indicates the formation of dimers with coordinated phosphonic groups.  The pH-metrically detd. species were confirmed by ³¹P-{¹H} and ¹H NMR titrns. of the systems involving Pd^II and Pt^II.